Air conditioner

ABSTRACT

An air conditioner includes a direct-current (DC) power supply, a compressor, and a compressor driving device that converts a current supplied from the DC power supply into an alternate-current (AC) for driving the compressor. The DC power supply energizes the driving device through a center conductor and an outer conductor of a shield cable. This structure allows the driving device not to include a capacitor for smoothing a power current, and to suppress surge voltages and electromagnetic-wave radiation, thus providing an air-conditioner including a compact size and light-weighted compressor driving device.

TECHNICAL FIELD

[0001] The present invention relates to an air conditioner equipped withan electric compressor and an electric compressor driving device.

BACKGROUND ART

[0002] A conventional electric compressor driving device used in a caris described hereinafter with reference to drawings. FIG. 15(a) shows aperspective view illustrating an appearance of an electric compressordriving device. Case 24 made of metal has a waterproof construction andaccommodates the device. Coupling-line output port 47 which has also awaterproof structure and is mounted to case 24 passes coupling line 55therethrough. Coupling line 55 includes two wires coupled to a battery,e.g., a direct-current (DC) power supply of approximately 300V, threewires coupled to an electric compressor, two wires coupled to a 12Vpower supply, and three wires carrying controlling signals and coupledto an air-conditioner controller.

[0003] In case 24, an inverter circuit converting a current from thebattery into an alternate-current (AC) current is located. This invertercircuit generates heat due to DC/AC converting loss. This heatdissipates into cooling water running through water-cooling tube 56mounted to case 24. The heat dissipation is not limited to the watercooling method, but an air cooling method can be used.

[0004] The above construction allows the electric compressor drivingdevice to be placed in a car with few restrictions, so that the drivingdevice can be disposed at a place away from the power supply, thebattery.

[0005]FIG. 15(b) illustrates the inside of case 24 of the electriccompressor driving device. Circuit board 57 having electric componentsmounted thereon and electrolytic capacitor 41 are located in case 24.Capacitor 41 is generally used as a power-current smoothing capacitorfor smoothing the current supplied from the battery to the invertercircuit. An outline of the appearance is shown as line 53.

[0006]FIG. 16 shows a perspective view illustrating circuit board 57shown in FIG. 15(b) and its related components. Circuit board 57 iscoupled to an inverter circuit 54 as an inverter block which generates aheat greater than other components, so that inverter circuit 54 ismounted to a cooling structure related to water-cooling tube 56.

[0007]FIG. 17 shows a circuit diagram of the electric compressor drivingdevice.

[0008] As shown in the drawing, battery 1 is coupled to compressordriving device 5 as a power supply through current-carrying device 2.Compressor driving device 5 includes inverter circuit 9 and electrolyticcapacitor 41 for smoothing the current supplied from battery 1 toinverter circuit 9.

[0009] Inverter circuit 9 is coupled to a load, i.e., electriccompressor 23. Current-carrying device 2 charges electrolytic capacitor41 through charging resistor 10 up to a voltage of battery 1, and thencloses main relay 11 for passing the current from battery 1 to invertercircuit 9. Current-carrying device 2 may be built in compressor drivingdevice 5.

[0010] A voltage supplied from battery 1 to compressor driving device 5is divided by upper bleeder resistor 13 and lower bleeder resistor 14,is insulated by voltage detector 16, and is then fed into invertercontrolling microprocessor 19. The current passing through invertercircuit 9 is detected by current sensor 15, is insulated by currentdetector 17, and is fed into inverter controlling microprocessor 19.

[0011] Air-conditioner controller 21 calculates a capacity (such as arotation speed) of compressor 23 necessary for an air-conditioner, andthe capacity is input to microprocessor 19 via communication circuit 20.

[0012] Inverter controlling microprocessor 19 sends signals to gatedriver 18 based on at least the inputs, thereby activating switchingelements of inverter circuit 9 for driving compressor 23.

[0013] Gate driver 18 electrically insulates inverter circuit 9 frommicroprocessor 19. Inverter controlling microprocessor 19 receivessequential temperature data supplied from a thermistor temperaturesensor of compressor 23. Switching power supply 12 produces a power forgate driver 18 and others. Current sensor 15 includes a current-carryingcoil having an inductance component. This coil produces magnetic fielddetected by a Hall element, so that a current is determined.

[0014] This is not shown in the drawings, but a traction motor drivingdevice is coupled to compressor driving device 5 in parallel, andcurrent-carrying device 2 works similarly on a current-smoothingcapacitor and an inverter circuit both equipped to the traction motordriving device. 12V power supply 22 is used as a power supply mainly forinverter controlling microprocessor 19 and communication circuit 20. 12Vpower supply 22 is also used as a power supply for many electricdevices, such as air-conditioner controller 21, audio equipment, and anavigation system. 12V power supply 22 is electrically insulated frombattery 1; and is however powered from battery 1 via a DC converter (notshown).

[0015]FIG. 18(a) shows a current flowing into inverter circuit 9, andFIG. 18(b) shows a current flowing into compressor driving device 5.

[0016] The waveform of the current flowing into inverter circuit 9 islike a rectangular wave. The waveform of the current flowing intocompressor driving device 5 includes a constant current although havingripples due to the current flowing into inverter circuit 9 smoothed byelectrolytic capacitor 41. Actual waveforms are more complicated, andFIG. 18 shows just outlines. As shown in FIG. 18(c), a DC voltage ofbattery 1 is applied to inverter circuit 9.

[0017]FIG. 19 is a schematic diagram of electric compressor 23 shown inFIG. 17. Compressor 23 includes metallic case 8 accommodatingcompressing mechanism 4 and motor 7. Refrigerant is sucked from intake45, and motor 7 drives compressing mechanism 4 (a scroll compressingmechanism), so that the refrigerant is compressed.

[0018] The compressed refrigerant cools motor 7 before being dischargedfrom outlet 46. Terminal 27 coupled to a winding of motor 7 incompressor 23 is connected to compressor driving device 5 shown in FIG.17.

[0019] Electrolytic capacitor 41 discussed above has a large size toincrease the size of the compressor driving device and to make thedriving device heavy. Electrolytic capacitor 41 is vulnerable tovibrations and heat, thus preventing the compressor driving device fromhaving an improved vibration proof and heat resistance.

[0020] A vehicle having a limited space, such as a compact electricvehicle and a hybrid electric vehicle, requires small components mountedin the vehicle. Further, the hybrid electric vehicle has a smaller spacesince having a space for an engine. Thus, no electrolytic capacitor 4 bemounted in the vehicle is proposed, but the following problems occur inthis case.

[0021] The current supplied from battery 1 to inverter circuit 9 wouldnot be smoothed without electrolytic capacitor 41. Then, the current ofrectangular waveform passing through a power supply lead wire radiateselectromagnetic-wave noises. As a result, a surge voltage is generatedin the power supply lead wire, thereby damaging the circuit ofcompressor driving device 5.

[0022]FIG. 20 shows a circuit diagram in which electrolytic capacitor 41is excluded (detailed structure is omitted). The case and junctionconnectors lengthen the power supply lead wire, so that a large andunstable inductance component 58 is generated in the lead wire.

[0023] Since the current is not smoothed by electrolytic capacitor 41shown in FIG. 17, the current shown in FIG. 21(a) and flowing intoinverter circuit 9 passes through the power supply lead wire. Thiscurrent passes through inductance component 58, so that surge occurs asshown in FIG. 21(c) when the current is turned off.

[0024] This surge has a high voltage and may damage inverter circuit 9.Electrolytic capacitor 41 shortens the path for the current flowing intoinverter circuit 9 just between capacitor 41 and circuit 9, so that theinductance between capacitor 41 and circuit 9 is small enough not togenerate surge as shown in FIG. 18(c).

[0025] The current shown in FIG. 21(b) has a high frequency component,and the power supply lead wire radiates electromagnetic wave noises whenthis current passing through the wire.

[0026] The present invention addresses the foregoing problems, and aimsto provide an air-conditioner equipped with a reliable electriccompressor driving device which has a small size and light weight anddoes not generate electromagnetic noises or a surge voltage.

SUMMARY OF THE INVENTION

[0027] In order to solve the foregoing problems, an air conditioneraccording to the present invention includes a direct-current (DC) powersupply, an electric compressor, and an electric compressor drivingdevice that converts the current supplied from the DC power supply intoan alternate-current (AC) current for driving the compressor. A centerconductor and an outer conductor of a shield cable is used for feeding acurrent from the DC power supply to the electric compressor drivingdevice.

[0028] This configuration cancels a magnetic field produced by a currentflowing through the center conductor of shield cable and anothermagnetic field produced by a current flowing through the outer conductorsince the center conductor and the outer conductor share the centeraxis.

[0029] Therefore, the cable has an inductance of substantially zero,thus allowing the driving device to suppressing a surge voltage and aradiated electromagnetic wave without an electrolytic capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a circuit diagram of an essential part of anair-conditioner in accordance with exemplary embodiment 1 of the presentinvention.

[0031]FIG. 2(a) illustrates a structure of a shield cable used in thecircuit.

[0032]FIG. 2(b) shows directions of magnetic field in the shield cableused in the circuit.

[0033]FIG. 3 is a graph indicating inductances of portions of thecircuit.

[0034]FIG. 4(a) shows a perspective view illustrating the appearance ofan electric compressor driving device of the air-conditioner.

[0035]FIG. 4(b) shows a perspective view illustrating the inside of theelectric compressor driving device.

[0036]FIG. 5(a) shows a waveform of a current flowing into an invertercircuit of the electric compressor driving device.

[0037]FIG. 5(b) shows a waveform of a current flowing into the electriccompressor driving device.

[0038]FIG. 5(c) shows a waveform of a voltage applied to the invertercircuit of the electric compressor driving device.

[0039]FIG. 6 is a circuit diagram of an essential part of anair-conditioner in accordance with exemplary embodiment 2 of theinvention.

[0040]FIG. 7(a) shows a waveform of a current flowing into an invertercircuit of an electric compressor driving device in accordance withembodiment 2.

[0041]FIG. 7(b) shows a waveform of a voltage applied to the invertercircuit of the electric compressor driving device.

[0042]FIG. 8 shows a perspective view of essential parts of a relaycontact of the electric compressor driving device.

[0043]FIG. 9 is a circuit diagram of an essential part of anair-conditioner in accordance with exemplary embodiment 3 of theinvention.

[0044]FIG. 10 shows a construction of a parallel-line cable used in thecircuit.

[0045]FIG. 11 is a circuit diagram of an essential part of anair-conditioner in accordance with exemplary embodiment 4 of theinvention.

[0046]FIG. 12 is a circuit diagram of an essential part of an airconditioner in accordance with exemplary embodiment 5 of the invention.

[0047]FIG. 13 shows a construction of a double shield cable used in thecircuit.

[0048]FIG. 14 shows a partial cut-away front view of an electriccompressor incorporating a driving device of the air conditioner.

[0049]FIG. 15(a) shows a perspective view illustrating an appearance ofan electric compressor driving device of a conventional air conditioner.

[0050]FIG. 15(b) shows a perspective view illustrating the inside of theelectric compressor driving device.

[0051]FIG. 16 shows an exploded perspective view for illustrating acircuit board and its related components in the electric compressordriving device.

[0052]FIG. 17 shows essential parts of a circuit diagram including theelectric compressor driving device.

[0053]FIG. 18(a) shows a waveform of a current flowing into an invertercircuit of the electric compressor driving device.

[0054]FIG. 18(b) shows a waveform of a current flowing into the electriccompressor driving device.

[0055]FIG. 18(c) shows a waveform of a voltage applied to the invertercircuit of the electric compressor driving device.

[0056]FIG. 19 shows a partial cut-away front view of a conventionalelectric compressor.

[0057]FIG. 20 is a circuit diagram excluding a smoothing electrolyticcapacitor of the electric compressor driving device, and indicating aninductance component.

[0058]FIG. 21(a) shows a waveform of a current flowing into an invertercircuit of the electric compressor driving device.

[0059]FIG. 21(b) shows a waveform of a current flowing into the electriccompressor driving device.

[0060]FIG. 21(c) shows a waveform of a voltage applied to the invertercircuit of the electric compressor driving device.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0061] An air conditioner according to exemplary embodiments of thepresent invention will be described hereinafter with reference to theaccompanying drawings.

[0062] (Exemplary Embodiment 1)

[0063]FIG. 1 is a circuit diagram of an electric compressor drivingdevice. As shown in FIG. 1, the power supply lead wire is formed of asingle shield cable 29 and electrolytic capacitor 41 is excluded, andelectrolytic capacitor 3 is however located at a side of battery 1.Those points are different from the conventional circuit shown in FIG.17.

[0064] If a power-supply impedance of battery 1 is small enough, noelectrolytic capacitor 3 is needed. In shield cable 29, center conductor30 is assigned to a positive side, and outer conductor 31 is assigned toa negative side.

[0065]FIG. 2(a) illustrates a construction of shield cable 29 and outerconductor 31 surrounds center conductor 30. FIG. 2(b) shows directionsof magnetic field of shield cable 29. Since the direction of the currentflowing through center conductor 30 is opposite to the direction of thecurrent flowing through outer conductor 31, magnetic field 32 producedby the current through center conductor 30 cancels magnetic field 33produced by the current through outer conductor 31. Electromagnetic waveis thus not radiated, and inductance of shield cable 29 becomes small.

[0066] The graph of FIG. 3 shows inductance values of wires andcomponents. The inductances are measured for the same connected lengthof the wires. Two lead wires of lm, a shield cable, a parallel-linecable, a twisted-pair cable of lm are prepared. The inductances aremeasured in μH. The lead wire has a larger inductance, and theinductance varies depending on an interval between the lead wires. Theinterval of 200 mm provides the inductance of 1.8 μH. A closer interval(equivalent to the parallel-line cable) provides an inductance of 0.5μH, thus having a difference of 3.6 times. Therefore, the lead wirecauses the inductances to be a difficulty of specified, so that areliable design is not obtainable.

[0067] The shield cable exhibits a small inductance. In the shieldcable, the distance between center conductor 30 and outer conductor 31stays constant, so that the inductance can be specified and a reliabledesign can be achieved. A parallel connection of a number “n” of theshield cables reduces the total inductance to 1/n.

[0068] In the conventional circuit shown in FIG. 15, the connectingwires between inverter circuit 54 and electrolytic capacitor 41 exhibitan inductance of 0.9 μH at an interval of 10 mm and a length of 20 cm.If the connecting wires are replaced with a shield cable (0.1 μH), theshield cable can extend up to 180 cm at which the inductance reaches thesame value (0.9 μH).

[0069] In the case that electrolytic capacitor 41 is excluded andelectrolytic capacitor 3 is located at a side of battery 1, the distancebetween inverter circuit 54 and electrolytic capacitor 3 can extend upto 180 cm.

[0070] Since the shield cable is a single line, the cable can be handledeasier than the two lead wires, and the shield cable can be bentflexibly, so that the shield cable allows to be located more flexiblythan a bus-bar (an elongated metal strip).

[0071]FIG. 4(a) shows a perspective view illustrating the appearance ofan electric compressor driving device, and FIG. 4(b) shows a perspectiveview of the inside the electric compressor driving device.

[0072] Since the driving device does not include electrolytic capacitor41, case 26 can be smaller than conventional case 24 shown in FIG.15(a). A connecting wire 51 includes one shield cable coupled to battery1, three wires coupled to an electric compressor, and three wires forcarrying control signals to an air-conditioner controller. Theconnecting wires are taken out from outlet 47 in a water-proofstructure. Reference numeral 56 denotes a water-cooling tube mounted tocase 26, and circuit board 57 is placed in case 26.

[0073] Since switching power supply 12 located in the driving device 5produces a voltage of 12V (described later referring to FIG. 6),connecting wire 51 does not include two wires coupled to a 12V powersupply.

[0074]FIG. 5(a) shows a current flowing into inverter circuit 9. Thecurrent is similar to that of the conventional circuit. FIG. 5(b) showsa current flowing into the compressor driving device. This current isdifferent from that of the conventional circuit since the current is notsmoothed due to no electrolytic capacitor 41, and thus the current issimilar to that shown in FIG. 5(a). FIG. 5(c) shows a voltage applied toinverter circuit 9. The inductance of shield cable 29 is smaller thanthat of the conventional circuit. Therefore, under the condition of thesame length of the lead wires between inverter circuit 54 andelectrolytic capacitor 3, a surge voltage shown in FIG. 5(c) issubstantially proportionate to the inductance, thus becoming smallerthan that of the conventional circuit shown in FIG. 21(c).

[0075] (Exemplary Embodiment. 2)

[0076]FIG. 6 shows an electric circuit of an electric compressor drivingdevice. This driving device differs from that shown in FIG. 1 in thefollowing points: Current sensor 15, voltage detector 16, and currentdetector 17 are deleted from the device shown in FIG. 1, and currentdetecting resistor 42, integrating resistor 43, integrating capacitor44, sub-relay 48, and film capacitor 28 are added instead. 12V powersupply 22 is not connected to driving device 5.

[0077] Inverter controlling microprocessor 19, which has been powered by12V power supply 22 in FIG. 1, is powered by switching power supply 12instead. Microprocessor 19 shares a ground with battery 1. Communicationcircuit 20 communicates with air-conditioner controller 21 in aninsulated condition with a photo-coupler. A voltage divided by upperbleeder resistor 13 and lower bleeder resistor 14 can be directly fedinto microprocessor 19.

[0078] A detected current can be directly fed into microprocessor 19using a voltage generated across current-detecting resistor 42 (shuntresistor). The detected current is used as protection-halt signal, sothat it may not be input to microprocessor 19, but it may be processedin a hardware-circuit.

[0079] When an average of the detected current is needed, a valueintegrated by integrating resistor 43 and integrating capacitor 44 maybe directly input to microprocessor 19. As shown as inductances of wiresand components in FIG. 3, the inductance of current-detecting resistor42 (shunt resistor) is close to zero (0), so that a surge voltage can bereduced more than that of the circuit with current sensor 15.

[0080]FIG. 8 shows a construction of a relay contact of sub-relay 48provided to a power supply line. Parallel flat relay-contact plates 49face each other (sub-relay contact 50 is placed at upper side). Thisconfiguration allows currents flowing in opposite directions to cancelthe magnetic fields, thus suppressing the inductance to a small value.

[0081] Next, an operation of film capacitor 28 is described hereinafter.

[0082]FIG. 7(a) shows a current flowing into inverter circuit 9. Thiscurrent is similar to that of the conventional circuit. FIG. 7(b) showsa voltage applied to inverter circuit 9. This voltage includes resonantvoltages of a small peak value since film capacitor 28 resonates withthe inductance of shield cable 29, thereby producing the resonantvoltage instead of a steep surge voltage. This is different from thevoltage shown in FIG. 20(c) and the voltage of embodiment 1 shown inFIG. 5(c). Thus, the surge voltage becomes small enough not to damagethe circuit of compressor driving device 5.

[0083] When film capacitor 28 is installed to the circuit, a capacitanceof the capacitor can be exactly specified since the inductance of theshield cable is specified. Therefore, the capacitance of film capacitor28 may not be excessive larger than necessary, thereby allowing filmcapacity 28 to be small.

[0084] Current detecting resistor 42 is placed at the right side of filmcapacitor 28 in order to prevent a resonant current from flowing. Filmcapacitor 28 includes a dielectric material mainly of plastic film andan electrode of metal foil. The capacitance of the capacitor is smallerthan that of an electrolytic capacitor; and has excellent high-frequencycharacteristics, which can absorb the surge voltage discussed above.

[0085] Film capacitor 28 can be replaced by a ceramic capacitorincluding a dielectric material mainly of ceramics and an electrodecoated with metallic film. Both types of capacitors have vibration proofand heat proof better than those of the electrolytic capacitor becauseof their constructions.

[0086] The electrolytic capacitor may restore a voltage even afterdischarged. The compressor driving device equipped with electrolyticcapacitor 41 generates a discharging spark between capacitors 41 and 3when the power supply is connected. This phenomenon causes a fuse-blownor adversely affects the operation. According to embodiment 2, noelectrolytic capacitor 41 is used, so that the driving device is freefrom this problem.

[0087] In this embodiment, an electrolytic capacitor is used assmoothing capacitor 3; however, it is not limited to the electrolyticcapacitor. A similar advantage can be obtained if shield cable 29 isreplaced by a parallel-line cable.

[0088] (Exemplary Embodiment 3)

[0089]FIG. 9 shows a circuit diagram of electric compressor drivingdevice in accordance with exemplary embodiment 3 of the presentinvention. A power supply lead wire employs parallel-line cable 34. Thisis a different point from the circuit shown in FIG. 1. FIG. 10 shows aconfiguration of parallel-line cable 34 shown in FIG. 9.

[0090] In parallel-line cable 34, two conductors 36 are parallel withresin 35 that is flexible and electrically insulating. It is not limitedto this shape, but two conductors may be applied with a tape or extendthrough a vinyl tube for forming the parallel-line cable. As shown inFIG. 3, the parallel-line cable have a small inductance, but theinductance is larger than that of a shield cable. In the parallel-linecable, a distance between the two conductors is kept constant, so thatthe inductance is also kept constant. Thus, a reliable design isachievable because since the inductance can be specified. Theparallel-line cable provides better workability than the two lead wires,and the parallel-line cable can be terminated easier than the shieldcable.

[0091] (Exemplary Embodiment 4)

[0092]FIG. 11 shows a circuit diagram of an electric compressor drivingdevice. A power supply lead wire employs a twisted-pair cable 37, whichis different from the cable of the circuit shown in FIG. 1. Two leadwires are twisted and fixed by tape 25.

[0093] As shown in FIG. 3, the twisted-pair cable has the sameinductance as that of the parallel-line cable. The twisted-pair cableincludes two lead wires twisted, so that the distance between the twolead wires is kept constant, thereby having an inductance specified andallowing a reliable design. The twisted-pair cable can be formed by justtwisting lead wires, so that the twisted-pair cable may be fabricatedeasier than the shield cable or the parallel-line cable.

[0094] (Exemplary Embodiment 5)

[0095]FIG. 12 shows a circuit diagram of an electric compressor drivingdevice employing double-shield cable 39. FIG. 13 shows a configurationof double-shield cable 39.

[0096] Instead of shield cable 29 employed in the circuit of the drivingdevice shown in FIG. 1, double-shield cable 39 is used. Outer mostconductor 38 is grounded to a car body via grounding wire 40.

[0097] This cable is used for suppressing electromagnetic-wave radiationcaused by a potential difference between a ground of the car body and apower supply system of battery 1. A single shield cable can only cancelmagnetic fields caused by currents, but cannot suppress theelectromagnetic-wave radiation. Outer most conductor 38 is thus groundedto the car-body, thereby shielding the electromagnetic-wave radiation.

[0098] Battery 1 is used as a power supply for driving the car, so thatit produces a high voltage, and is isolated from the ground of the carbody for safety. Battery 1 can be grounded via a metal case ofcompressor 23 or compressor driving device 5.

[0099] Parallel-lines cable 34 shown in FIG. 9 and twisted-pair cable 37may be provided with a shield cover for covering the cables, and thecover may be grounded.

[0100] (Exemplary Embodiment 6)

[0101]FIG. 14 illustrates compressor driving device 5 installed toclosely contact the left side of electric compressor 23. Compressor 23has a basic configuration identical to that used in the conventional airconditionaer shown in FIG. 19.

[0102] Case 6 of driving device 5 is modified from case 26 shown in FIG.4 so that driving device can be mounted to compressor 23. Inverter block54, i.e., a heat source, dissipates heat to metal case 8 of compressor23 via case 6.

[0103] Terminal 27 is coupled to an output section of inverter block 54.Since compressor driving device 5 is not equipped with electrolyticcapacitor 41, device 5 can be small and free from restriction due to theshape of capacitor 41, so that driving device 5 can be modified easilyto be mounted to compressor 23.

[0104] Electrolytic capacitor 41 is vulnerable to vibration, and has alife varying according to heat. The compressor without capacitor 41allows driving-device 5 to have less countermeasures (vibration proofand heat proof construction) against vibration and heat delivered fromcompressor 23.

[0105] Coupling wires 52 include one shield cable to battery 1, threewires carrying control signals to an air-conditioner controller.Switching power supply 12 installed in driving device 5 can produce 12V,so that two power-supply lead wires necessary for a 12V power supply areomitted.

[0106] Inverter block 54 is cooled with refrigerant in compressor 23 viametal case 8, however, it can be cooled by a construction, such as watercooling or air cooling. Compressor 23 should be placed around a tube inwhich the refrigerant flows, so that compressor 23 is obliged to be awayfrom battery 1, however, a small inductance of shield cable 29 enablesthe compressor to be place at this position.

INDUSTRIAL APPLICABILITY

[0107] As described, a center conductor and an outer conductor of ashield cable are used for supplying a power to an electric-compressordriving device from a direct-current (DC) power supply. The center andouter conductors allows the driving device to suppress surge voltagesand electromagnetic-wave radiation even without a smoothing capacitorwhich smoothes a power current, thus providing an air conditionerincluding a compact and light-weighted compressor driving device.

[0108] In addition to the above construction, double outer conductorsare prepared in the shield cable, and the outer most conductor is usedfor shielding electromagnetic wave. This construction suppresseselectromagnetic-wave radiation caused by an electric potentialdifference between a grounding of a power supply system and a groundingof a car body.

[0109] In addition to the foregoing construction, the driving device ismounted to the compressor, so that an electrolytic capacitor can beomitted from the driving device. Thus, the driving device is free fromrestrictions on the reliability and the service life caused byvibrations of the driving motor of the compressor and heat generated bycompressing the refrigerant. As a result, the compressor driving devicecan be small and free from restriction of the size of the electrolyticcapacitor (capacitor for smoothing a power current).

[0110] The foregoing construction allows a circuit board to be modifiedin shape easily, so that the driving device can be mounted to thecompressor. This structure can omit lead wires between the drivingdevice and the compressor, and omit a cooling structure (such as watercooling or air cooling) by dissipating heat to the refrigerant. Thisstructure further reduces the size and weight of the driving device.

1. An air conditioner comprising: a direct-current (DC) power supply; anelectric compressor; an electric-compressor driving device forconverting a current supplied from said DC power supply to analternate-current (AC) current for driving said electric compressor; anda shield cable including a center conductor and an outer conductor forsupplying said current from said DC power supply to saidelectric-compressor driving device.
 2. The air conditioner of claim 1,wherein said outer conductor of said shield cable includes double outerconductors, and an outer most conductor is used for shielding anelectromagnetic wave.
 3. An air conditioner comprising: a direct-current(DC) power supply; an electric compressor; an electric-compressordriving device for converting a current supplied from said DC powersupply into an alternate-current (AC) current for driving said electriccompressor; and one of a parallel-line cable and a twisted-pair cablefor supplying said current from said DC power supply to saidelectric-compressor driving device.
 4. The air conditioner of any one ofclaims 1 to 3, wherein said electric-compressor driving device ismounted to said compressor.
 5. The air conditioner of any one of claims1 to 3, wherein said electric-compressor driving device includes aninverter circuit, and no current smoothing capacitor is provided at apower supply side of said inverter circuit included in saidelectric-compressor driving device.